The long-term goal of this research plan is to identify those factors responsible for the expression of alpha-fetoprotein in normal and transformed cells of the mouse. Alpha-fetoprotein is a major constituent of serum in the developing mouse fetus. During intrauterine life, it is synthesized in the yolk sac and the liver. After birth the concentration of alpha-fetoprotein in serum decreases until, in the adult, it is less than 0.01% of that in fetal serum. Re-expression of alpha-fetoprotein has been detected in a number of disease states, the most significant and consistent of which are carcinoma of the liver, liver injury and teratacarcinomas. In fact, an elevated serum alpha-fetoprotein level is a widely used diagnostic test for these diseases. In order to understand the link between the expression of alpha-fetoprotein in fetal liver and in neoplastic cells, and its absence in adult mouse liver, the genetic sequences which code for alpha-fetoprotein in the mouse genome will be purified and cloned into a bacteriophage lambda derivative, lambda gtWES.lambda B. To accomplish this, alpha-fetoprotein mRNA will be partially purified from fetal liver and used as a substrate for the synthesis of double-stranded DNA by reverse transcriptase and DNA polymerase I. The DNA transcript will be inserted by the poly(dA)-poly(T) method into the plasmid vehicle pCR1. The hybrid plasmid will serve as a monoclonal probe for the detection and biochemical purification of alpha-fetoprotein sequences in mouse genomic DNA by RPC-5 chromatography and agarose gel electrophoresis. Following approximately 1000-fold enrichment of these sequences, they will be cloned into lambda gtWES.lambda B via restriction enzyme Eco R1 cleavage sites. The cloned sequences will be characterized by restriction enzyme analysis and electron microscopy.